1. Field of the Invention
This invention relates to methods of manufacture of MOSFET devices and the devices and more particularly to the pattern of spacers employed for manufacture of contacts for LDD devices.
2. Description of Related Art
U.S. Pat. No. 5,208,472 of Su et al. for "Double Spacer Salicide MOS Device and Method" shows a double spacer MOS device and method. The first spacer layer is composed of silicon dioxide and the second spacer layer is formed of an unidentified dielectric layer which is deposited as a blanket layer which is etched back to form spacers which remain in the final product.
U.S. Pat. No. 5,494,838 of Chang et al. for "Process of Making EEPROM Memory Device Having a Sidewall Spacer Floating Gate Electrode" shows another double spacer where the spacers are not removed by the SAC etch as in the present invention. The first spacer layer is composed of silicon nitride and the second spacer layer is formed of silicon oxide.
U.S. Pat. No. 5,468,665 of Lee et al. for "Process for Making a Semiconductor MOS Transistor Employing a Temporary Spacer" shows a method that uses a temporary spacer to inhibit ion implantation during formation of a first high concentration first dopant buried layer in the substrate in the source/drain regions.
Conventional fabrication of LDD spacers in MOSFET devices consists of gate patterning, oxide deposition and oxide etch back to form oxide spacers along gate lines. As the line width decreases and layers of interconnections increase in ICs, the oxide spacers are replaced by silicon nitride spacers for Self-Aligned Contact (SAC) formation for the advantages of wide photolithographic overlay windows and contact isolation. However, the simple Si.sub.3 N.sub.4 spacers in SAC processes show their limitations between the open area of contacts and LDD spacer length as shown in FIG. 1.
Prior art processing techniques of LDD spacer formation using using double spacers have the disadvantages as follows:
There are narrow processing windows for contact etching and area due to the SAC process where contact area is limited only by LDD spacers. PA1 LDD length is difficult to adjust because of the configuration of the spacers.